Photoluminescence enhancement of quantum dots on Ag nanoneedles

Abstract

Noble metal nanostructure allows us to tune optical and electrical properties, which has high utility for real-world application. We studied surface plasmon-induced emission of semiconductor quantum dots (QDs) on engineered metallic nanostructures. Highly passive organic ZnS-capped CdSe QDs were spin-coated on poly-(methyl methacrylate)-covered Ag films, which brought QDs near the metallic surface. We obtained the enhanced electromagnetic field and reduced fluorescence lifetimes from CdSe/ZnS QDs due to the strong coupling of emitter wave function with the Ag plasmon resonance. Observed changes include a six-fold increase in the fluorescence intensity and striking reduction in fluorescence lifetimes of CdSe/ZnS QDs on rough Ag nanoneedle compared to the case of smooth surfaces. The advantages of using those nanocomposites are expected for high-efficiency light-emitting diodes, platform fabrication of biological and environmental monitoring, and high-contrast imaging.

Figure 1

SEM images of Ag-nNDLs at × 50,000 (A) and × 150,000 (B). Topographical AFM images of Ag films: (C) smooth Ag substrate and (D) rough Ag-nNDLs. Insets show the depth profiles along each line.

Figure 2

AFM images of smooth (A) and rough (B) substrate after QD coating.

Figure 3

UV and PL spectra of CdSe/ZnS QDs (A) and UV–vis spectra of Ag-nNDLS (B). a, smooth Ag nanofilm; b, Ag-nNDL. (C) Absorbance spectra of QDs on each film. (D) Fluorescence spectra of QDs in chloroform at the same absorbance intensity.

Figure 4

PL spectra for CdSe/ZnS nanocrystals on silver surfaces (A). a, smooth surface; b, rough surface. (B) Time profile of PL signal for CdSe/ZnS nanocrystals on Ag surfaces.